This invention relates to a mobile communication method and a mobile communication system in which technique of an asynchronous transfer mode (ATM) multiplexing is applied or used to a transmission between a base station and an exchange station or a base station control apparatus.
In prior art, technique of a synchronous transfer mode (STM) multiplexing is used as a transmission path interface between a base station and a mobile communication exchange station. In the manner well known in the art, the STM multiplexing is one of a time division multiplexing (TDM) system and is a system which periodically distributes time-divided channels into which an original channel is temporality divided. The STM multiplexing has a frame structure in which each frame is divided into a plurality of time slots. There is, as the transmission path interface in the STM multiplexing, a 1.5 Mbit/s highway interface or a 2 Mbit/s highway interface. The 1.5 Mbit/s highway interface has a frame structure in which each frame is divided into twenty-four time slots while the 2 Mbit/s highway interface has,a frame structure in which each frame is divided into thirty-two time slots. In the 1.5 Mbit/s or 2 Mbit/s highway interface, one time slot in each frame is exclusively assigned for control of the base station. Alternatively, two time slots in each frame may be exclusively assigned for control of the base station for redundancy structure.
In addition, in prior art, the mobile communication exchange station is provided with a plurality of base station control signal terminating equipments which are fixedly connected to host call processing processors in one-to-one correspondence fashion. In addition, the base stations are connected to the base station control signal terminating equipments in one-to-one correspondence fashion. Accordingly, connection between a base station and a call processing processor has a structure of one-to-one connection fashion.
As a result, if subscribers concentrate to a particular area to which a group of base stations belongs, congestion between the base station control signal terminating equipment and the call processing processor may occur. It will be assumed that there is a plurality of control links between the base station and the base station control signal terminating equipment. In this event, the number of time slots for user traffic in each frame decreases and it results in degrading a transmission efficiency of the user traffic between the base station and the mobile communication exchange station.
Various mobile communication systems of the type are already known. By way of example, a mobile communication system is disclosed in Japanese Unexamined Patent Publication of Tokkai No. Hei 10-42,337 or JP-A 10-042337. The mobile communication system according to JP-A 10-042337 is a mobile communication system which performs ATM transmission of data transfer between a base station and a mobile communication exchange station. According to JP-A 10-042337, it is possible for the mobile communication system to execute site diversity to a mobile station during soft handover and to execute selective synthesis of received signals in low delay in the mobile communication exchange station. Transmitted from base stations to a mobile communication exchange station in layered cells, received data are received in ATM cell receiving arrangements and thereafter decomposed into short cells in short cell converting arrangements. After a short cell header is converted into a mobile station identifying ID in a UCI interpreting arrangement, a distributing arrangement distributes short cells including received data from a mobile station during soft handover. After a frame sorting arrangement obtains short cells including received data of every user, the short cells are supplied to frame selecting arrangements to select the received data having larger likelihood. However, the mobile communication system disclosed in JP-A 10-042337 does not take congestion of call processing and transmission efficiency between the base station and the mobile communication exchange station into consideration.
Another mobile communication system is disclosed in Japanese Unexamined Patent Publication of Tokkai No. Hei 9-322,235 or JP-A 09-322235. According to JP-A 09-322235, it is possible to provide a mobile communication system in which the transmission efficiency of an ATM link in the system is enhanced. The mobile communication system according to JP-A 09-322235 is composed of a portable set (PS) , base stations (BSs) , and a mobile exchange center (MSC). In the mobile communication system, site diversity every frame is carried out by using ATM links between the base stations and the mobile exchange center. In this event, the base station is provided with a frame transfer discrimination arrangement for discriminating whether a frame received from the portable set is aborted or is transferred to the mobile exchange center based on reliability information and with a threshold storage arrangement for storing a threshold used for discrimination of the frame transfer discrimination arrangement. As a result, a frame with low reliability is aborted by the base station and it is therefore possible to make the transmission between the base stations and the mobile exchange center efficient. However, the mobile communication system disclosed in JP-A 09-322235 does not take congestion of call processing and overhead of a call processing processor in an exchange station or in a base station control apparatus into consideration.
It is therefore an object of this invention to provide a mobile communication method and a mobile communication system, which are capable of avoiding congestion of call processing.
It is another object of this invention to provide a mobile communication method and a mobile communication system of the type described, which are capable of improving transmission efficiency.
It is still another object of this invention to provide, which is capable of provide a mobile communication method and a mobile communication system of the type described, which are capable of eliminating much of overhead of a call processing processor in an exchange station or in a base station control apparatus.
Other objects of this invention will become clear as the description proceeds.
According to a first aspect of this invention, a mobile communication method is for use in a mobile communication system for carrying out transmission between a plurality of base stations and an exchange station using an asynchronous transfer mode (ATM). The exchange station includes N call processing processors where N represents a positive integer which is not less than two. The mobile communication method comprises the steps of establishing N call processing virtual connection links between each of the stations and the exchange station, and of controlling, in response to outgoing calls successively generated by said base stations, the call processing by the N call processing processors in order by changing the N call processing virtual connection links in order.
According to a second aspect of this invention, a mobile communication method is for use in a mobile communication system for carrying out transmission between a plurality of base stations and a base station control apparatus using an asynchronous transfer mode (ATM). The base station control apparatus includes N call processing processors where N represents a positive integer which is not less than two. The mobile communication method comprises the steps of establishing N call processing virtual connection links between each of the base stations and the exchange station, and of controlling, in response to outgoing calls successively generated by the base stations, the call processing by the N call processing processors in order by changing the N call processing virtual connection links in order.
According to a third aspect of this invention, a mobile communication method is for use in a mobile communication system comprising a mobile station, a plurality of base stations, and an exchange station connected to the base stations. The exchange station comprises N call processing processors where N represents a positive integer which is not less than two. The mobile communication method comprises the steps of informing, on reception of an outgoing call for the mobile station, the mobile station of an node number for identifying the exchange station actually connected to the mobile station via a particular base station and a processor number for identifying the call processing processor actually carrying out a call processing to make the mobile station hold the node number and the processor number as a held node number and a held processor number, of sending, when the mobile station carries out handover, the held node number and the held processor number from the mobile station to a new base station destined for the handover, and of selecting, in the exchange station managing the new base station, a call processing processor in accordance with load distribution order to make the call processing processor inherit a call processing.
According to a fourth aspect of this invention, a mobile communication method is for use in a mobile communication system comprising a mobile station, a plurality of base stations, a base station control apparatus for controlling the base stations, and an exchange station connected to the base station control apparatus. The base station control apparatus comprises N call processing processors where N represents a positive integer which is not less than two. The mobile communication method comprises the steps of informing, on reception of an outgoing call for the mobile station, the mobile station of a node number for identifying said base station control apparatus actually connected to the mobile station via a particular base station and a processor number for identifying the call processing processor actually carrying out a call processing to make the mobile station hold the node number and the processor number as a held node number and a held processor number, of sending, when the mobile station carries out handover, the held node number and the held processor number from the mobile station to a new base station destined for the handover, and of selecting, in the base station control apparatus managing the new base station, a call processing processor in accordance with load distribution order to make the call processing processor inherit a call processing.
According to a fifth aspect of this invention, a mobile communication system is for carrying out transmission between a plurality of base stations and an exchange station using an asynchronous transfer mode (ATM) . The exchange station comprises a plurality of primary ATM interfaces for carrying out connection of the base stations and another node, an ATM switch, N call processing processors for carrying out call control processing, where N represents a positive integer which is not less than two, a common signaling processing processor for carrying out communication control between the other node and the exchange station, an operational maintenance processor for managing the N call processing processors and the common signaling processing processor and for carrying out a path setting control for the ATM switch, and a plurality of primary base station control signal terminating equipments, disposed between the ATM switch and respective ones of the N call processing processors, the common signaling processing processor, and the operational maintenance processor, for setting links between each of the base stations and the other node and the exchange station. Each of the base stations comprises a radio interface section for radio communication between the mobile station and the base station in question, a secondary base station control signal terminating equipment for establishing an operational maintenance virtual connection link between the operational maintenance processor and the secondary base station control signal terminating equipment and N call processing virtual connection links between the N call processing processors and the secondary base station control signal terminating equipment, a central processing unit for controlling the radio interface section and the secondary base station control signal terminating equipment to select the call processing virtual connection link in order in response to an outgoing call, a secondary ATM interface for carrying out connection between the exchange station and the base station in question, and a multiplexing and demultiplexing unit for multiplexing and demultiplexing signals between the secondary ATM interface and the radio interface section and the secondary base station control signal terminating equipment.
According to a sixth aspect of this invention, a mobile communication system is for carrying out transmission between a plurality of base stations and a base station control apparatus using an asynchronous transfer mode (ATM). The base station control apparatus comprises a plurality of primary ATM interfaces for carrying out connection of the base stations and another node, an ATM switch, N call processing processors for carrying out call control processing, where N represents a positive integer which is not less than two, a common signaling processing processor for carrying out communication control between the another node and the base station control apparatus, an operational maintenance processor for managing the N call processing processors and the common signaling processing processor and for carrying out a path setting control for the ATM switch, primary base station control signal terminating equipments, disposed between the ATM switch and respective ones of the N call processing processors, the common signaling processing processor, and the operational maintenance processor, for setting links between each of the base station and the other node and the base station control apparatus. Each of the base stations comprises a radio interface section for radio communication between the mobile station and the base station in question, a secondary base station control signal terminating equipment for establishing an operational maintenance virtual connection link between the operational maintenance processor and the secondary base station control signal terminating equipment and call processing virtual connection links between the N call processing processors and the secondary base station control signal terminating equipment, a central processing unit for controlling the radio interface section and the secondary base station control signal terminating equipment to select the call processing virtual connection link in order in response to an outgoing call, a secondary ATM interface for carrying out connection between the exchange station and the base station in question, and a multiplexing and demultiplexing unit for multiplexing and demultiplexing signals between the secondary ATM interface and the radio interface section and the secondary base station control signal terminating equipment.